diff --git a/storage/mysql/log_storage.go b/storage/mysql/log_storage.go
index 2d57c7d4fd..045b803b07 100644
--- a/storage/mysql/log_storage.go
+++ b/storage/mysql/log_storage.go
@@ -82,10 +82,11 @@ const (
 )
 
 var (
-	once             sync.Once
-	queuedCounter    monitoring.Counter
-	queuedDupCounter monitoring.Counter
-	dequeuedCounter  monitoring.Counter
+	once                    sync.Once
+	queuedCounter           monitoring.Counter
+	queuedDupCounter        monitoring.Counter
+	dequeuedCounter         monitoring.Counter
+	clearedStmtCacheCounter monitoring.Counter
 
 	queueLatency            monitoring.Histogram
 	queueInsertLatency      monitoring.Histogram
@@ -101,6 +102,7 @@ func createMetrics(mf monitoring.MetricFactory) {
 	queuedCounter = mf.NewCounter("mysql_queued_leaves", "Number of leaves queued", logIDLabel)
 	queuedDupCounter = mf.NewCounter("mysql_queued_dup_leaves", "Number of duplicate leaves queued", logIDLabel)
 	dequeuedCounter = mf.NewCounter("mysql_dequeued_leaves", "Number of leaves dequeued", logIDLabel)
+	clearedStmtCacheCounter = mf.NewCounter("mysql_cleared_prepared-statement_caches", "Number of times the prepared-statement cache has been cleared")
 
 	queueLatency = mf.NewHistogram("mysql_queue_leaves_latency", "Latency of queue leaves operation in seconds", logIDLabel)
 	queueInsertLatency = mf.NewHistogram("mysql_queue_leaves_latency_insert", "Latency of insertion part of queue leaves operation in seconds", logIDLabel)
@@ -741,6 +743,7 @@ func (t *logTreeTX) getLeavesByHashInternal(ctx context.Context, leafHashes [][]
 	args = append(args, t.treeID)
 	rows, err := stx.QueryContext(ctx, args...)
 	if err != nil {
+		t.ls.clearStmtCache()
 		klog.Warningf("Query() %s hash = %v", desc, err)
 		return nil, err
 	}
diff --git a/storage/mysql/tree_storage.go b/storage/mysql/tree_storage.go
index ffb0159cd6..6cfda3ea5a 100644
--- a/storage/mysql/tree_storage.go
+++ b/storage/mysql/tree_storage.go
@@ -47,9 +47,9 @@ const (
 	 n.TreeId = ? AND n.SubtreeRevision <= ?
 	GROUP BY n.TreeId, n.SubtreeId
  ) AS x
- INNER JOIN Subtree 
- ON Subtree.SubtreeId = x.SubtreeId 
- AND Subtree.SubtreeRevision = x.MaxRevision 
+ INNER JOIN Subtree
+ ON Subtree.SubtreeId = x.SubtreeId
+ AND Subtree.SubtreeRevision = x.MaxRevision
  AND Subtree.TreeId = x.TreeId
  AND Subtree.TreeId = ?`
 	placeholderSQL = "<placeholder>"
@@ -104,6 +104,25 @@ func expandPlaceholderSQL(sql string, num int, first, rest string) string {
 	return strings.Replace(sql, placeholderSQL, parameters, 1)
 }
 
+// clearStmtCache clear up all sql.Stmt in cache
+func (m *mySQLTreeStorage) clearStmtCache() {
+	m.statementMutex.Lock()
+	defer m.statementMutex.Unlock()
+
+	klog.Info("Clearing all prepared statements")
+
+	for _, ns := range m.statements {
+		for _, s := range ns {
+			if err := s.Close(); err != nil {
+				klog.Warningf("Failed to close stmt: %s", err)
+			}
+		}
+	}
+
+	m.statements = make(map[string]map[int]*sql.Stmt)
+	clearedStmtCacheCounter.Inc()
+}
+
 // getStmt creates and caches sql.Stmt structs based on the passed in statement
 // and number of bound arguments.
 // TODO(al,martin): consider pulling this all out as a separate unit for reuse
@@ -114,8 +133,6 @@ func (m *mySQLTreeStorage) getStmt(ctx context.Context, statement string, num in
 
 	if m.statements[statement] != nil {
 		if m.statements[statement][num] != nil {
-			// TODO(al,martin): we'll possibly need to expire Stmts from the cache,
-			// e.g. when DB connections break etc.
 			return m.statements[statement][num], nil
 		}
 	} else {
@@ -200,6 +217,7 @@ func (t *treeTX) getSubtrees(ctx context.Context, treeRevision int64, ids [][]by
 
 	rows, err := stx.QueryContext(ctx, args...)
 	if err != nil {
+		t.ts.clearStmtCache()
 		klog.Warningf("Failed to get merkle subtrees: %s", err)
 		return nil, err
 	}
@@ -296,6 +314,7 @@ func (t *treeTX) storeSubtrees(ctx context.Context, subtrees []*storagepb.Subtre
 
 	r, err := stx.ExecContext(ctx, args...)
 	if err != nil {
+		t.ts.clearStmtCache()
 		klog.Warningf("Failed to set merkle subtrees: %s", err)
 		return err
 	}